1. The Field of Invention
The present invention relates to a method and product for terminating electrical conductors and in particular to a method and product which combine insulation piercing and solder technology.
2. The Prior Art
There are many acceptable ways to join electrical conductors to electrical terminals including soldering, crimping, brazing, welding and, in the last decade, a method generally referred to an insulation displacement, commonly referred to as IDC for insulation displacement connection. Each of these techniques has its place according to parameters of material cost, cost of the labor for effecting the joint and according to the resulting reliability, all in the context of a given environment of use. Put more directly, one can take less care and spend less on interconnecting wires to drive displays or motors in toys that sell for less than a day's pay than one might for like components used in a space shuttle where not only a fortune is at stake, but life itself.
In general, the bulk of electrical terminations have been made by soldering and crimping with IDC now becoming more widely used because of productivity improvement implicit in the technique. The advantages of solder include a potential for excellent reliability and low cost, when performed properly and employed in large volume production utilizing sophisticated soldering equipment where the solder process can be controlled rather exactly and the parts can be readily designed to fit the process. When neither the geometry of the parts can be controlled nor high volume exists to underwrite volume production equipment, hand soldering can be and is widely utilized. It is there that the five variables in soldering become most critical and sensitive to variability. These five include having the right solder, the right cleanliness of surfaces to be soldered, the right fixturing to hold things still, the right pressure on the parts for heat transfer and the right amount of heat or dwell time of heat application. In the article "Soldering Technology--A Decade of Developments," International Metals Review, 1984, Volume 29, Number 2, by C. J. Thwaites, all of the foregoing aspects are mentioned in some detail with as thorough a bibliography as one is likely to find, though in citing this useful article it must be stated that not all of the 449 cited references have been studied.
When one or more of the above discussed five critical requirements for a good solder joint vary too much, trouble will surely follow. For example, when one uses the wrong solder relative to the surface of the metal or geometry of the parts to be soldered, all sorts of problems can occur--the solder will not wick well or wet to the surfaces, potential corrosion due to the electrical disparity of metals may result, the solder will not bond well and so forth. If the wrong flux is used to clean the surfaces to be soldered, poor joints are almost inevitable. Acid fluxes, suitable for plumbing, can literally eat up the relatively fragile parts used for electronic components. Totally neutral acids, which may be preferred for the foregoing reasons, may not break through the surface oxides intrinsic to the metal surfaces of the parts or those oxides developed in time by the environment and duration of inventory. A case of nerves and the resulting jitter, while solder is liquid, can easily spoil a solder joint and, of course, too much heat will also do so. Pores and fractures in a solder joint evidence an over application of heat caused by sudden out gassing. Lumpy appearance and cold joints evidence too little heat. In pot or wave solder baths, surface dross can and does plague all operations. An accidental introduction of organics, or build up in time of such ingredients to brighten solder, can cause dewetting, voiding, oxidation, and poor appearance problems. In a word, bad chemistry, bad metallurgy, bad practices all can limit solder as an electrical connection medium.
The art of crimping is usually performed by pressure application, in a tool, on a portion of a metal terminal to inelastically deform such about a bare electrical wire. The terminal/tool system assures excellent terminal/wire joints repeatedly with little skill required. Crimping typically takes a great deal of energy and even with small wires/terminal crimps can demand 70 to 100 inch-pounds of work with die forces frequently exceeding 1000 to 1500 pounds. Larger sizes of terminal/wire indeed require forces of many thousands of pounds. Moreover, crimping usually calls for precision displacement of dies to effect the necessary deformation and tolerances between 0.001 and 0.003 inches are not uncommon. Thus high force and close tolerance characterizes most quality crimps. As can be appreciated, high forces and close tolerances mean precision die surfaces and precision tool linkages which inescapeably means cost. Additionally, high forces call for tooling dies that are quite strong and capable of bearing repeated forces and frictional engagements of the metal deformation of terminals. That fact dictates a certain size limitation, width and height, beef, if you will, limiting how close terminals may be fixed in connectors and still be crimped by practical dies. It limits how many wires can be crimped simultaneously without having to have a multi-ton force mechanism such as a press. In a word, high force, precision and size of crimping dies all act as major recognized limitations on crimping as a termination technology. For a more complete understanding of the foregoing, reference is made to the following text: "Physical Design of Electrical Systems," Volume III, Integrated Devices in Connection Technology, Chapter 10; authored by members of The Bell Telephone Laboratories, copyright 1971 Prentiss Hall Inc., Englewood Cliffs, N.J.
The concept of IDC involves stuffing an insulated wire into a slot in a metal portion of a terminal. It has evolved in two ways for separate reasons. An early use of IDC is shown in Patent #3,320,354 to J. E. Marley issued May 16, 1967. There, insulation displacement was employed to essentially effect stripping so as to handle very small solid wires where removal of insulation proved difficult and time consuming. A second aspect of IDC relates to the situation where, by the use of insulation displacement, improved productivity could be obtained due to the fact that relatively large multiples of wires could be terminated simultaneously, essentially because the forces of termination are relatively low, being measured in the tens of pounds for wire gauges on the order of 18 to 26 AWG, rather than in hundreds of pounds or thousands of pounds as in the case of crimp technology. Reference may be made to U.S. Pat. No. 3,012,219 to E. J. Levin et al issued Dec. 5, 1961, for a description of this latter type of IDC use.
In fact, IDC use has been more spurred by increased productivity than by merely its advantage in stripping insulation. Productivity improvements utilizing IDC have resulted in labor cost reductions per termination on the order of 50 to 70 percent, particularly where the IDC concept is employed in pre-loaded multiple connectors.
The main problem with IDC is a perception that what goes in easily comes out easily. Despite efforts to ally this perception by fixes with metal or plastic insulation gripping structures, many users have refrained from employing IDC technology. The success and reliability of proven solder and crimp technology has, to some extent, intimidated the use of IDC concepts.
For a good overall understanding of the IDC technology, reference is made to AMP incorporated publication HB5351, revision B, "Introduction of AMP Insulation Displacement Techniques and Products" published by AMP Incorporated, copyright 1976, 1979 by Arlen Crandall.
In summary, solder can be an excellent electrical terminal terminating technique but one must control the five critical factors or else suffer bad joints, crimp works well with little skill but takes high forces and precision tooling and is limited in center-to-center application and for multiple wire applications; and IDC gives productivity increases and self stripping but can come apart if one can pull or push the wire out of the slot that is the basis of the technology.